Second Fear Period:
6 to 14 Months While the 8 to 12 week puppy fear period is in some cases hardly noticed by puppy owners, the second fear period appears to have a much bigger impact. Rover has grown now and if he is a large breed he may even weigh 100 pounds or more!
This fear period is believed to be tied to the dog's sexual maturity and growth spurts. This means that in large breeds it may develop later compared to a smaller dog. Often, this stage is also known as "teenage flakiness" according Ellen Dodgein her article "Critical Periods in Canine Development" published in the Weimaraner Magazine. October. 1989.
In the wild, dogs at this age are allowed to go on hunts with the rest of the pack. At this stage, it is important for them to learn to stick with the pack for safety, but they also need to learn about fear since they need fear for survival purposes.The message to the puppy is to run away if something unfamiliar approaches them, explain Wendy and Jack Volhard in the book Dog Training for Dummies.
Reactivity levels rise during this stage causing the dog to act defensively, become protective and more territorial. Owners often report the fear seems to pop out of nowhere. Dogs appear fearful of novel stimuli or stimuli met before but that did not trigger significant reactions.
As in the first fear period, it is best to avoid traumatic experiences during this time such as shipping dogs on a plane and any other overwhelming experience. Because at this stage the owner may be dealing with a dog barking and lunging and pulling on the leash, this fear period has a bigger impact, causing the owner to worry about the dog's behavior.
How to Make Things Better: Continue socializing as much as possible but without exposing your dog to overwhelming situations Create positive associations through counter-conditioning Build confidence through training and confidence building sports and exercises Avoid traumatic experiences during this delicate phase.
Counter-Condition
If your dog acts fearfully towards a certain stimuli you can try to change your dog's emotional response by using treats or anything the dog finds rewarding. The moment your dog sees the threatening stimulus give treats, the moment the threatening stimulus disappears take the treats away. The same can be done with sounds the dog finds startling, make the sound become a cue that a tasty treat is coming. What if your dog won't take treats? Most likely, the stimulus is too scary and the dog is over threshold. Don't Overwhelm,
Desensitize!
Work, under the threshold from a distance your dog or puppy does not react fearfully and is able to take treats. If you overwhelm and flood your puppy, you risk sensitizing your puppy which means you make him more fearful. Don' t force your puppy to interact with the feared stimulus; rather allow him to investigate whatever he fears on his own and remember to praise/reward any initiative your puppy or dog takes!
Socialize, socialize, socialize
Fear periods are part of a dog's developmental stages. The more your dog is exposed to stimuli and learns there is nothing to be scared about, the more confident he will be in the future when he will encounter anything intimidating. While the window of opportunity for the puppy socialization phase closes at around 14 to 16 weeks, socialization opportunties should virtually never end.
Don't Punish the Fear
Last but not least, avoid punishing the fear. It is appears that the majority of dog aggressive displays are due to fear; therefore, by punishing the behavior you will be only exacerbating the fear. Ignore the fear and let your dog build confidence by letting him investigate things on his own when he is ready and praising for the effort. Use force-free behavior modification such as desensitization and counterconditioning
Bron: https://pethelpful.com/dogs/Dog-Behavior-Understanding-Fear-Periods-in-Dogs